There are many applications in education and industry in which it is desirable to supply electrical power to a plurality of remotely located devices. It is conventional practice to provide for connection of each of these devices to a source of utility power, such as 120 VAC typically with an external ac/dc converter. However, electrical codes require that utility power cables be fed through metal conduits or raceways separate from signal and data cables, undesirably increasing the cost and complexity of installation. For example, in wireless local area network (LAN) applications, each of the transceivers is conventionally connected to a utility power source by utility power cabling fed through conduits and raceways separate from the data and signal cabling.
It is a general object of the present invention to provide a power distribution system and apparatus that eliminate the requirement in the prior art for separate utility power cabling to the remote powered devices, such as LAN transceivers in the specific embodiment of the invention herein disclosed. A more specific object of the present invention is to provide a power distribution system and apparatus of the described character in which power is fed to the remote devices at low voltage level--e.g., in the range of 8 to 28 volts d.c.--that allows the power to be applied to the remote apparatus through the same cabling as carries the signal data. Another and yet more specific object of the present invention is to provide an apparatus for controlling distribution of d.c. power to a plurality of remote d.c.-powered devices in which a plurality of independent d.c. power supplies are provided for supplying primary and backup power to the remote devices, and that includes capability for detecting failure at any one of the primary power supplies and automatically connecting the associated remote devices to the backup supply. A further object of the present invention is to provide an apparatus of the described character that includes facility for locally and/or remotely indicating a power supply failure condition, preferably including an audible failure indication and means for selectively disabling the audible failure indication either remotely or at the power distribution apparatus.
Apparatus for controlling distribution of d.c. power to a plurality of remote d.c. -powered devices in accordance with the present invention includes a plurality of independent d.c. power supplies with facility for connecting the supplies to a source of electrical power such as a utility power line. A plurality of electrical switches are operable in a first mode of operation for connecting a first number of the power supplies to apparatus outputs for connection to the remote devices. Failure detection circuitry detects power failure at one or more of the first number of power supplies, and operates one or more of the switches in a second mode of operation to connect a second number of the power supplies different from the first number to the apparatus outputs in place of the one or more power supplies at which failure is indicated.
In a presently preferred implementation of the invention, there is provided apparatus for controlling distribution of d.c. power to a plurality of remote d.c.-powered LAN transceivers, which includes a plurality of first or primary d.c. power supplies and at least one second or backup d.c. power supply, all having means for connection to a source of electrical power to supply output d.c. power independently of each other. A plurality of electrical switches are each operable in a first mode of operation to connect one of the primary power supplies to at least one set of output terminals for connection to a remote transceiver. Comparator circuits compare the output voltage at each of the primary power supplies to output voltage at the backup power supply to indicate a failure condition at one of the primary supplies. Circuitry is responsive to such a failure indication for operating one or more of the electrical switches in a second mode of operation in which at least one set of output terminals is connected to the backup power supply. Thus, the output terminals and LAN transceivers connected thereto are continuously supplied with uninterrupted electrical power in the event of a power failure at one or more of the primary power supplies.